(1) Field of the Invention
The present invention relates to a method for separating and purifying lactoferrin, which is a pharmacologically important milk protein having various physiological activities, from milk containing lactoferrin.
(2) Description of the Prior Art
Lactoferrin is an iron-binding glycoprotein present in an exocrine liquid such as milk and has a variety of physiological activities such as bateriostasis against pathogenic bacteria, adjusting function of leukocyte differentiation, build-up function of germicidal power, multiplicative function of lymphocyte and adjusting function of iron absorption. For that reason, it can be said that lactoferrin is a milk protein which is important not only from a nutritional viewpoint but also a pharmacological viewpoint.
As a result, many attempts have heretofore been made to develop methods for separating and purifying lactoferrin from milk. However, since lactoferrin is a protein having a very reactive molecular structure and interacting with other milk proteins, it has been difficult to separate and purify lactoferrin in a high purity and in a high yield by a simple and easy operation.
In other words, in order to separate high-purity lactoferrin, an intricate process and a long period of time is necessary. In addition, the recovery efficiency of lactoferrin is disadvantageously low.
Recently, a separating and purifying method for lactoferrin has been reported in which a raw liquid is passed through an affinity column where heparin having physiological affinity to lactoferrin is fixed on a carrier for chromatography such as Cephalose CL-6B (made by Pharmacia Labs., Inc.) with the aid of CNBr or the like, whereby lactoferrin is separated and purified therefrom (Blackberg, L. et al, FEBS LETT., 109, p. 180, 1980).
However, heparin is extracted and purified from the livers or intestines of pigs, cattle or the like, and differences in the source of extraction lead to differences in heparin properties. For this reason, it is hard to obtain a great deal of heparin having uniform properties. Further, heparin is expensive. As a result, the method of separating and purifying lactoferrin from milk by the use of the affinity carrier for chromatography having heparin bound and fixed thereto can be practiced only on an experimental scale. In other words, the above suggested known method is impracticable on an industrial scale. Further, the above method has the problem that heparin fixed on the carrier might be peeled therefrom and inconveniently mixed with separated lactoferrin on occasion.